This K01 application is designed to prepare the applicant with the skills necessary to establish an independent research program on the study of systemic lupus erythematosus (SLE). SLE is an autoimmune disease of unknown cause which mainly afflicts women in their child bearing years and affects multiple organ systems of the body. T cell dysfunction due to abnormally altered intracellular signaling events is thought to be central in the pathogenesis of this disease. A critical signaling molecule known as the CD3 zeta chain is expressed in abnormally low amounts in the T cells of SLE patients, and this defect contributes to the poor functional capacity of the SLE T cells. Expression of an abnormal alternatively spliced (AS) form of the CD3 zeta mRNA with poor half life is a contributor to the reduced expression of zeta chain in SLE T cells. Aberrant splicing is a common feature observed in SLE and involves other critical genes involved in T cell signaling, migration, and cytokine production and the regulation of these genes has not been characterized. To understand the regulation of the CD3 zeta alternative splicing, the applicant used a discovery approach and identified several proteins binding to the CD3 zeta mRNA. Among these proteins, a promising candidate is the serine arginine (SR) family member Alternative Splicing Factor/Splicing Factor 2 (ASF/SF2). The applicant published that in T cells from healthy individuals, ASF/SF2 regulates CD3 zeta chain expression by suppressing production of the AS isoform. Examination of T cells from SLE patients revealed that patients had reduced expression of ASF/SF2 suggesting that aberrant ASF/SF2 expression may contribute to their defective T cell function. Additionally, the ASF/SF2 expression levels appeared to inversely correlate with the disease activity of SLE patients. The applicant's preliminary studies have shown a novel role for the splicing regulator ASF/SF2 in T cell physiology with a potential role in SLE pathophysiology. Based on the preliminary evidence, the hypothesis of this project is that ASF/SF2 regulates human T cell function and may represent a contributor to the SLE T cell defect. Toward the hypothesis, this project is aimed to understand the role of ASF/SF2 in human T lymphocytes and to determine whether ASF/SF2 may represent a disease marker in SLE. Methods will include biochemical analyses of human T cells and the development of a cell line to enable controlled expression of ASF/SF2. The specific aims of the project are 1) To determine whether TCR stimulation regulates ASF/SF2 expression and activity in human T lymphocytes 2) To determine how ASF/SF2 regulates T cell function and 3) To determine whether ASF/SF2 expression levels in SLE T cells may represent a disease marker. To accomplish these aims, the applicant will need to expand her technical and intellectual skills in cellular and molecular immunology and become proficient in the design, interpretation and analysis of studies in SLE patients. The research environment at Beth Israel Deaconess Medical Center and the other affiliates of the Harvard Medical School system will provide the applicant with the resources to reach her goals within 5 years.